During the first 10-40 seconds of cold start engine operation, an internal combustion engine is typically commanded to operate at lean air/fuel ratio (A/F) with significantly retarded spark timing due to stringent emission regulations. This mode of engine operation, however, poses significant challenges especially in light of variability in product componentry and the in-use fuel driveability index. A key reason for this sensitivity is that during such cold start conditions, neither the exhaust gas oxygen (EGO) sensor nor the catalyst is active so the engine operation needs to be controlled under total open loop condition. At the same time, operating at lean A/F with significant spark retard causes the combustion to become significantly more unstable, resulting in large torque fluctuations which create various forms of undesirable noise, vibration and harshness (NVH).
Thus, there exists a need to operate the engine at lean A/F during engine cold start under a closed loop condition in order to insure combustion remains stable.